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STORMWATER TREATMENT AT CRITICAL AREAS: EVALUATION OF FILTRATION MEDIA
Citation:
Clark, S. AND R. E. Pitt. STORMWATER TREATMENT AT CRITICAL AREAS: EVALUATION OF FILTRATION MEDIA. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/R-00/010 (NTIS PB2000-104209), 2000.
Impact/Purpose:
information
Description:
Past research has identified urban runoff as a major contributor to the degradation of urban streams and rivers. Filtration, especially "slow" filtration, is of interest for stormwater runoff treatment because filters will work on intermittent flows without significant loss of capability. Stormwater filters currently in operation typically use the following media -- sand, compost, and peat. This research tested the capabilities of the media currently in use, plus others with known filtering capability (activated carbon, zeolite, a cotton milling waste, and a wood waste), in both controlled laboratory and field conditions. Influent and effluent samples from each filter column were analyzed for toxicity, turbidity, conductivity, pH, major anions and cations, and particle size distribution for each test. This research demonstrated that physical clogging of the filters occurred well before the sorptive capacity of most media is reached when stormwater runoff is filtered without adequate pre-treatment. If adequate pre-settling is done, the solids remaining in the runoff are generally very small (colloidal). These filters are capable of removing many of the colloidal sized particles; however, the percent removals (measured as suspended solids removal) are smaller when there are fewer larger particles in the influent. Testing using laboratory-scale columns showed that an activated carbon-sand filter is the best at removing the stormwater pollutants. In terms of chemical capacity, results of the testing showed that the activated carbon, peat moss, zeolite and compost were the most efficient media at removing the toxicants from the runoff and retaining them during subsequent flushings with clean distilled water. In all cases, the media had to be mixed with sand to maintain adequate flow rates.